Apparatus for sensing various types of photographic color films and for converting an image into a video signal are well known in the art. With the development of relatively low cost, reliable solid state image sensors there has been increasing interest in the development of film video players for displaying film images such as those present on color slides or color negatives on television monitors and receivers. With the availability of such sensors there has arisen an interest in composing a video image corresponding to only a portion of a film image and for displaying or recording such a video image.
A primary reason for the interest in composing selected video images constituting a portion of a film image is that the resolution of the commonly used photographic film formats is substantially greater than standard television resolution by factors of approximately four to ten times. As will be appreciated, the full available resolution of these film formats is not effectively used at normal magnification where the full frame image substantially fills the solid state image sensor so that the video image effectively just fills the display of the television monitor or receiver. The excess resolution available in these film formats can be advantageously utilized by providing a film video player with means such as zoom optics for selectively changing the magnification of the video image and thus the displayed image with respect to the film image. Since in its magnified form the video image and resultant display constitutes only a portion of the film frame image, such film video players also preferably effect relative vertical and horizontal translation between the film image and the video image. More advanced composing or editing functions can be carried out where it is possible to effect relative rotation between the film image and the video image.
A common approach in the design of film video players of this type contemplates the use of fixed apparatus for mounting a slide or film negative presenting a film image and a fixed sensor spaced a distance therefrom along the optical axis of the system. Interposed between the fixed film image and fixed sensor is a multi-group variable focal length lens wherein one of the lens elements is movable axially along the optical axis to vary the focal length of the lens and thus provide a zoom capability.
Multi-group variable focal length lenses of this type suffer the disadvantage that they are relatively expensive. Such multi-group variable focal length lenses normally require the driving of a plurality of substantially fixed, complex cam surfaces to effect the zoom functions, and more specifically, establish and maintain focus as magnification changes. The cam surfaces are necessarily chosen to meet normal conditions for a particular system and cannot readily be altered or adjusted to accommodate manufacturing or assembly variations in variables such as the focal length of a particular lens or the exact plane where a film image or a sensor is mounted or oriented in a particular film video player. Normally, attempts to eliminate variables of this nature which degrade the performance of a film video player can be accomplished only by expensive adjustment or customizing procedures which must be employed for each individual unit being manufactured. Thus, the production of film video players employing multi-group variable focal length lenses involves extreme expense in terms of both the cost of the components employed and the labor required for assembly and adjustment due to the necessity for an essentially customized installation.
In film video player devices where the photographic film presenting the film image is moved horizontally and vertically to effect scan of the film image relative to the optical axis, significant ancillary problems are encountered. Such movement of the film carrying the film image creates mechanical difficulties in effecting quick film change which is highly desirable or in some instances essential in equipment of this type. In particular, whether slides or film negatives are employed, a moving slide or film holder makes it difficult if not impossible under reasonable cost constraints to design mechanisms for rapid loading and unloading of slides, film strips or other film segments. At the very least the utilization of known, inexpensive and proven slide and film change equipment is obviated. Thus, it is highly advantageous in devices of this type that the photographic film be presented in a mounting assembly which remains stationary.
U.S. Pat. Application Ser. No. 143,661 for "Film Video PLayer Apparatus", filed Jan. 13, 1988, proposes a film video player employing a fixed focal length lens and a plurality of stationary film image planes. The disclosed system creates a selectively composed video signal from a photographic film image by moving the lens and sensor axially along the optical axis of the system, by translating the sensor in two perpendicular directions relative to the film frame image, and by rotating the sensor relative to the film frame image. The present invention is generally directed to a device for advantageously establishing and maintaining the focus in such a film video player, irrespective of the magnification and without the need for cam surfaces.